Traditionally, emergency exits from public or private premises that receive the public have been fitted with locking means constituted by chains and padlocks. Such locking means have been found to be completely unsuitable since, for example, in the event of a fire it is not possible to open the emergency exits quickly and effectively.
Locks for unlocking emergency exits have therefore been provided that are capable of operating under remote control by an electrical current being interrupted, i.e. locks in which a door can be released only under the effect of energy stored within the lock, e.g. by means of a spring.
However, to be effective, the system for unlocking an emergency exit must not only be suitable for remote control by interrupting a current, it must also be capable of responding to release of the energy stored in the lock even, if the door is being subjected to significant pressure at the time of release, e.g. by panic-stricken users. This is particularly difficult to ensure in simple manner.
It may also be observed that in practice, an emergency exit from premises that receive the public nearly always has two quite distinct modes of operation:
when the public is present, generally in daytime, the emergency exit must be governed by regulations for ensuring personal safety, even at the expense of reduced security for property, and even though security for property continues to be the major worry of the person responsible for the security of the premises; and
when the public is absent, generally at night, the emergency exit returns to being an ordinary door, not subject to administrative constraints concerning personal safety, but with an obvious and increased function of protecting property.
Locks have already been proposed for closing emergency exits while satisfying safety regulations, which locks are such that a door is held in place by a device that retracts in the event of feed current being interrupted or whenever forces greater than some predetermined value (e.g. about 60 dN) are applied thereto. With respect to personal safety, such locks are satisfactory insofar as they are easily opened in an emergency, however they are not very effective at protecting property. It is therefore often necessary to add additional locking means thereto in order to reinforce the invulnerability of emergency exits to tampering, particularly when the public is absent.
Locks are also known having a lock-bolt driven by an electromagnet and implemented in such a manner that powering the electromagnet drives a metal part to interpose itself between the bolt and its keeper to prevent the door being opened. Simultaneously, this action compresses a return spring for returning the bolt into the body of the lock when the power supply to the electromagnet is interrupted. Users find that the strength of the bolt is quite satisfactory, however there is no chance of the spring unlocking the door if pressure is being exerted on the door at the moment the spring is required to act, thereby making the system incompatible with safety regulations that require an emergency exit to be capable of opening even when major pressure is being exerted on the door.
Safety devices are also known suitable for fitting to anti-panic bars. Such devices introduce a delay in the action of the anti-panic bar. When a user presses against a bar, the pressure does not act on means for unlocking the door, but rather starts a timeout of a few seconds' duration while simultaneously generating a remote alarm. If the user releases the bar, thinking that the door is locked, then the timeout starts again. However, if the user maintains pressure throughout the timeout, then at the end of the timeout the door unlocks. It may be observed that anti-panic bars, by the design of the locks on which they act, cannot be considered as constituting high security locking means. In addition, safety devices based on a timeout and on triggering a remote alarm suffer from the drawback of giving users thereof a great many false alarms coming from people, often with no evil intent, pressing against the bars either by mistake or by clumsiness.
Electromagnetic door-holders are also known which are not properly speaking locks at all. With this type of equipment, so long as power is delivered to an electromagnet fixed on the door frame, it holds a plate made of magnetic metal and fixed on the door. The attractive force of such devices is considerably less than the break-in resistance that can be expected of a good lock, so such devices cannot prevent a door being broken open by application of violent shocks. In addition, such equipment does not take account of the problem of providing locking when the public is not on the premises. From the above it can be seen that none of the prior art locks for use with emergency exits provides a satisfactory solution to all of the locking requirements both of their purchasers and of the authorities, since none of the prior locks solves the contradictions of the following requirements taken together:
unlocking in the event of a power failure and in the presence of the public, no unlocking when a power failure occurs while the public is not present;
very robust locking both day and night which nevertheless retracts reliably when required to even if several panic-stricken users are pressing frantically against the doors of an emergency exit; and
remotely controllable and very reliable changeover between public-present and public-absent modes of operation.
The present invention seeks to remedy the above-mentioned drawbacks and to take account of all of the requirements mentioned above so as to provide an effective locking device offering a very high degree of security in the absence of the public while nevertheless being very easily unlocked in the presence of the public and under remote control merely by interrupting the electrical power supply to the device, with changeover between a public-present mode of operation and a public-absent mode of operation being easily performed, preferably under manual or automatic remote control.